A small-sized fan motor is reduced in size and a single-phase motor having a single coil is used in consideration of cost burden. In this case, the single coil is wound in a quadrangular or triangular coreless/bobbinless type and mounted on a PCB as disclosed in Korean Registered Utility Model Publication No. 20-0296035 (Patent Document 1).
BLDC motors are synchronous motors with fast dynamic response, low rotor inertia and easy speed control.
When a brushless direct current (BLDC) motor is used as the single-phase motor, a Hall sensor for rotor position detection is required to detect the N-pole and S-pole magnetic poles of the rotor to generate a switching signal of the driving current to the stator coil and the Hall sensor is expensive. Therefore, it is preferable to use a driving circuit using only one Hall sensor.
In this case, in the case that a single Hall sensor is used, the magnetic pole of the Hall sensor is not detected when the Hall sensor is located at the interface of the rotor magnetic pole, and thus the current cannot be supplied to the stator coil. Therefore, there is a dead point at which the starting cannot be performed.
In such a single Hall sensor system, there are a method of using an auxiliary magnet so that a Hall sensor deviates from a magnetic pole interface (i.e., a neutral point) of the rotor by using a magnet for fixation to a stator as a self-starting strategy avoiding a dead point, a method of installing magnetic screws on a coil winding portion, and a method of using a special shape dead point prevention yoke as in Patent Document 1.
In the case of using a Hall sensor for rotor position detection for generating a switching signal of the driving current for the stator coil, the cost increase factor occurs since it is necessary to use an expensive Hall sensor and to mount the additional components for the self-starting. Therefore, there is a demand for a method of generating a rotor position signal while minimizing the cost increase factor without using the Hall sensor.
In addition, various sensorless motor driving methods have been proposed for detecting rotor position signals without using a Hall sensor. In this case, a back electromotive force (EMF) is detected using a neutral point in the case of a three-phase BLDC motor using a three-phase coil, and when a neutral point is not present, a virtual neutral point is configured to indirectly detect a back electromotive force (a back EMF), and compare the detected back electromotive force (EMF) with U, V, and W drive signals to obtain an output similar to the Hall sensor output.
However, in the case of a single-phase motor using a stator made of a single coil, the above-described method cannot be applied.
In the case of the single-phase motor, it is possible to employ a double winding method in which a main coil is wound first and a sensing coil for detecting the rotor position is wound once again and extended from each coil to be connected to the drive circuit. In this case, a back electromotive force (a back EMF) generated from the sensing coil at the time of rotor rotation is detected and the switching element of the motor driving circuit is driven based on the detected signal to determine the rotation direction.
However, such a double winding type stator has a disadvantage that it is difficult to use it because of its complicated structure and complicated winding. In addition, since the stator of the double wiring type uses a core type, it is difficult to realize a slim-type structure.
Meanwhile, fan motors used in electronic appliances such as computers and household appliances such as refrigerators largely employ outer rotor type fan motors that can be made compact in the radial direction and the axial direction in consideration of their installation space.
A conventional outer rotor type fan motor is a radial type motor and includes a motor portion and a fan portion that rotates at an outside of the motor portion by rotation of a rotating shaft of the motor portion.
In the outer rotor type fan motor, since the stator adopts the core type, the height of the motor cannot be reduced. Also, since the diameter of the bearing provided at the center of the stator and supporting the rotating shaft is limited, there is a problem that sufficient oil cannot be contained therein.
Korean Utility Model Application Publication No. 20-1987-0013976 (Patent Document 2) discloses an axial flow fan. In the axial fan disclosed in Patent Document 2, the motor is constituted by an axial type in which the field magnets of the rotary fan and the armature coils face each other. However, since the structure in which the air core type armature coils are disposed in the coil winding portion is employed, there is a problem that the height of the stator cannot be reduced anymore.
In addition, a stator of a fan motor disclosed in Korean Patent Laid-Open Publication No. 10-2000-0044146 (Patent Document 3) includes a stator yoke and a single-phase armature coil stacked on an upper portion of a PCB, and a bearing holder at a center of the PCB in which a pair of ball bearings are built in to support the rotating shaft. However, there is still a problem that the stator cannot be made in the form of a thin film.
Meanwhile, in the single-phase motor of Patent Document 1, the stator coil is composed of three rectilinear portions and three vertexes connecting the three rectilinear portions. Portions opposed to the magnets in the rectilinear portion of the stator coil form a magnetic field necessary for torque generation, but the vertexes serve only to connect the rectilinear portions and do not contribute to torque generation.
Since the conventional triangular stator coil has a small total area of the rectilinear portions of the coil (winding) and the portions where the magnets face when the rotor rotates, the torque for rotating the rotor is small. Finally, the conventional triangular stator coil does not have a coil pattern to effectively generate the torque.
Furthermore, in the case of a small fan, the coil is composed of fine wires in a general coil winding method in which a stator coil is wound on a bobbin, a stator coil is wound in a bobbinless type, or a stator coil is wound on a core. Therefore, when the thickness of the coil is constant in the start line and the end line, there is a problem that the start line and the end line may be broken due to careless handling or vibration during soldering the start line and the end line on the solder land or terminal, or the manual soldering process may be defective.
Meanwhile, when wireless power transmission (particularly, rapid charging) is performed to the terminal, the wireless charger generates a lot of heat in the transmission coil and the electronic component, and the charging efficiency is lowered. Accordingly, there is a need for a small, slim-type cooling fan for preventing temperature rise inside the wireless charger by an air cooling method.